An implantable mammary prosthesis includes a limpet buttress fill port structure. The fill port structure preferably comprises a shell, the shell including an opening, a compartment interior to the shell adapted to contain a filler. The limpet buttress is generally cup-shaped, and is disposed within the shell. The limpet buttress is preferably attached to the shell adjacent the opening to form a fluidic seal, optionally via a sealing flange. The limpet buttress may include one or more ribs, such as to provide structural support to the limpet buttress. Preferably, a reservoir is disposed external to the shell.